Abstract: To ensure normal advance and safe mining of working face containing small pit goaf, the technology of filling with repeated mining is introduced in this paper, that is, the inorganic materials are used to fill the small pit goaf first, which can form a cutting layer or key bearing layer inner the small pit goaf according to the position relation between the working face and goaf, and makes that it can maintain the stabilities of face roof and surrounding rock when the face passing through the small pit goaf. Then, the normal fully mechanized caving face is arranged for mining. In the paper, based on the mechanics structure of key bearing layer in small pit goaf during the process of repeated mining, and the mechanics model of weight drop and low speed impingement plate structure, we conducted systematic analysis on the mechanism of grouting filling in small pit goaf and the stability of regenerated key strata in the filled area of small pit by using mechanism analysis and theoretical calculation, and figured out the intension and thickness parameters of key bearing layer for maintaining the stability of face roof and surrounding rock around coal wall. The results show that applying the technology of grouting filling in layers to build key bearing layers in a certain thickness can maintain the stability of roof and coal wall areas when the working face mining through the small pit goaf.

Key words: small pit goaf, filling repeated mining, layered grouting, key bearing layer, stability